Need help with Pivot Table and Slicers to Group Columns

I am trying to make a bar graph with slicers and from what I understand, I first need to make a pivot table based on my data...

The issue I am running into is that I cant create a header for some of my columns..

In one column, I have cells that contain the names of my sales people, with the header "Sales Person".
To the right of it, I have a column that contains the name of the store that the sales person works at, with the header "Store".
The Next 12 columns to the right of that have the month abbreviated "JAN" "FEB" MAR" etc, and the cells below each month header contain how many units the sales people sold for that month.

What I want is a slicer named "Month" where I can select "JAN" for example, and see how many units every one sold in January, and then if I wanted to also filter by store, I could use the Store Slicer and select the Store & Month together...

I thought I could merge 12 cells above the abbreviated months and call the merged cell "months" and that would work, but it gives be and error when creating a pivot table.

I'll attach a screen shot so you can see what I'm looking at. There might be another way to get my desired result, and I'm happy to hear any ideas.

EXCEL PIVOT TABLE SLICER.PNG

Thank you!